Microstructure and Properties of CuW50Cr25 Composite

Abstract:

Article Preview

CuW50Cr25 composite prepared by infiltration was investigated. The results show that
the microstructure consists of four phases: W-rich and Cr-rich CuWCr solid solution as well as
Cr-rich and Cu-rich CrCu phases. The original Cr particles in the compact are replaced part by
Cu-rich CuCr phase and part by Cr-rich CrCu phase which is the first breakdown phase in the
course of the material’s arcing. The chopping current value of CuW50Cr25 composite is 2.4A and
arc duration is 4.01ms. These properties are much more excellent than counterpart of CuW70. The
breakdown strength is 2.31×108 V/m and comparable with the CrCu contact materials.

Abstract: A series of CuW60Cr15 composites with different Cr particle size ranging from 43μm
to147μm in diameter have been prepared by infiltration. The results show that the size of Cr
particles plays an important role on the microstructures and the properties of the CuW60Cr15
composite. Fine Cr particle changes not only the size of the isolated CrCu alloy zone but also the
structure of the skeletons of the composite obviously. Fine Cr particles increase not only the
maximum and the minimum but also the mean value of breakdown voltage. Although the maximum
value of chopping currents remains almost constant while Cr particles become finer, the minimum
and the mean values of chopping current discernible decrease in the CuW60Cr15 composites. It can
be seen from the SEM photos of the composites after arcing that the size and its location of the arc
spot determines the chopping current value of the composites.

Abstract: The Cu20W70Cr10 composites were fabricated by two methods which are the
conventional powder metallurgy, and mechanical alloying to prepare WCr compound powders,
followed by sintering and infiltration. The erosion behavior of CuWCr composites under
breakdown was investigated. The surfaces of the composites before and after erosion and the
mechanism of arc erosion were studied by scanning electron microscopy. The results show that the
CuWCr composites prepared by mechanical alloying have superfine microstructure, uniform
composition and high density, thus result in good characteristics of diffusing arcs and arc eroding
endurance. Arc erosion zones are dispersive and uniform on the surfaces with some flat eroding pits.
The Cu20W70Cr10 composites have excellent electrical properties such as high breakdown
voltage, low chopping current and long arc life.

Abstract: The CuWCr composites were respectively fabricated by the mixture of W and Cr and WCr alloyed powders, followed by sintering and infiltration. Vacuum arcs on CuWCr composites were observed by a digital high-speed video camera. The morphologies of the composites before and after arc erosion were characterized by a scanning electron microscope. The results show that the microstructure CuWCr composites prepared by WCr alloyed powders becomes finer and more uniform, and, thus, has good characteristics of diffusive arcs and arc erosion resistance. In addition, the composite prepared by WCr alloyed powders has excellent electrical properties such as high breakdown voltage, low chopping current and long arc life. Arc erosion zones of the CuWCr composite fabricated by WCr alloyed powders become more dispersive and uniform on the surfaces with some shallow erosion pits. During the course of arc evolution, the dispersed arcs are caused by the split of electrical arc.

Abstract: Cu-Cr contact material is used in medium voltage, high current vacuum interrupters. Vacuum interrupter is the heart of Vacuum Circuit breaker. Contact tips are usually made using powder metallurgical techniques in disk shape. These disks are machined to required dimensions and then hermitically sealed by vacuum brazing. The properties of the final contact tips are thus usually rarely studied. In the present study the properties before and after the vacuum sealing are compared in order to establish a correlation between them. The Cu-Cr contact tips were made under different compaction pressures, sintering temperatures and soaking time periods. Cu-Cr contacts were prepared by powder processing route and sintering in vacuum furnace at the temperatures of 1050°C for different soaking time period of 4, 6 and 8 Hrs. The samples were then subjected to simulated sealing cycle at temperatures (870 and 960°C). The electrical conductivity, hardness, microstructure and grain morphology of all the samples were studied. Properties of as-sintered and after sealing were analyzed and compared. The results of quantitative microscopy shows the better result on sintered sample soaked for 4 Hrs. The hardness and conductivity of the sample without brazing, varies between 79.9 - 83.8 HRF and 37.9 - 43.1% IACS respectively. The hardness and conductivity of the brazed sample varies between 52.5 - 63.42 HRF and 48.32 - 51.33 %IACS respectively.